Computer ?

Anyone know how the computer acts when it goes bad in these vans ? I've got a 95 with the 3800 engine with about 160,000 miles. The engine runs smooth as can be without a load but bucks & surges under load about 45 - 50 mph. The cooling fans come on whenever they feel like it which cause the temp to get pretty hot sporatically and run normally other times. The fans won't come on if it sits and idles. The temp just rises higher & higher. The trans TCC seems to lock up way too soon causing it to seem like it goes into high gear when you slow down to go around corners. It chugs like a manual trans in high gear at too slow a speed. I can't get the AC compressor clutch to kick on even though it seems to have plenty of R14 pressure. There are no codes, just an occasional 406 EGR linear pintle position error, which goes away for about a week when I clear it. I've replaced the plugs & wires and some rotten vacuum lines with no improvement. With all these problems & no codes, I'm at a loss as to where to start. Thanks.